1. Field of the Invention
The present invention pertains to tools for use in measuring and marking material, and, more particularly, to a transparent ruler having a non-removable, slip-resistant working surface.
2. Description of the Related Art
Transparent rulers having grid lines formed thereon are known for use in measuring and marking material, such as fabric, paper, plastic, and the like. These rulers are also used to guide a tool, such as a razor, knife, or rotary cutter, in cutting the material to desired sizes and shapes.
One such ruler is that described in U.S. Pat. No. 4,779,346 for a transparent measuring device that includes a plurality of continuous two-color lines of contrasting colors. In use, these lines are visible against a background of multiple colors, thus facilitating the measuring and marking of material.
To ensure accuracy, it is necessary that the ruler be firmly held in place with respect to the workpiece. Most rulers have a smooth planar bottom surface that will lie flat on the workpiece to be marked or cut. This smooth surface has the disadvantage of allowing the ruler to easily slip over the surface of the workpiece. Thus, a certain amount of force must be applied to a device to hold it in place on the workpiece. This frequently occurs on workpieces formed of or covered with a cloth or fabric material. In quilting applications, where large rulers are used to measure and mark material and to guide cutting tools on large pieces of fabric, it frequently becomes necessary to use both hands to hold the ruler in order to prevent it from slipping on the fabric. This makes it difficult for one person to measure or cut the fabric. Many times an individual will use a foot or knee to assist the one hand in applying pressure to the ruler in order to free the use of the other hand. This method is awkward and is not always feasible, such as in the case of handicapped persons or where the work surface is higher than the waist.
The disadvantage of the ruler described in U.S. Pat. No. 4,779,346 is that the working surface that is placed against the material is subject to slipping on the material. One device that attempts to overcome inadvertent slipping of the ruler is described in U.S. Pat. No. 5,829,150 issued to McEligot on May 1, 1998. Here, a sheet thick enough to guide a rotary cutter along one side and having an adhesive side is removably positioned on a rigid template material. This effectively forms a mechanical stop on the measuring device. The disadvantage is that the adhesive material easily collects dirt, lint, hair, and other material that reduces the adhesiveness and interferes with the use of the ruler. It also does not provide a non-slip surface but rather it forms a raised edge that can itself slide when placed on top of fabric.
Another device that attempts to address this slippage problem is a non-slip cutting ruler disclosed in U.S. Pat. No. 5,471,749, which teaches using retractable pins that secure the ruler to the fabric. This is a complex and potentially injury-causing approach that has not met with much success in the marketplace.
A further approach is to clamp the tool to the material, which is the subject of U.S. Pat. No. 4,875,667 that describes an elongate bar having a clamp at one end to brace the other end of the bar on a support surface. The other end of the bar is pushed down on a ruler and the underlying fabric. Unfortunately, this device can break the ruler when the bar is pressed down too hard. In addition, the bar is cumbersome to use and expensive.
Other methods have been employed to reduce slipping, such as: die-cut dots made from rubber, sandpaper, and cork; handles with suction cups to attach to the top surface of the tool; handles with pins that protrude through the plastic and into the fabric; weights; clear fingernail polish with salt; and ink with grit therein. These methods create one problem while solving another, including not providing enough grip, or gripping too much and snagging the fabric, scratching the work surface, not being transparent, wearing out, leaving adhesive on the ruler or the fabric, or cracking, crazing, or otherwise damaging the tool.